Liquid level controls for containers such as boilers are known as shown by U.S. Pat. No. 3,834,357 issued Sept. 10, 1974 to L. Kaczmarek et al. Level control circuits in which the electrical path through an electrode or probe is at a low AC level such as 24 volts is shown by U.S. Pat. No. 4,019,067 issued Apr. 19, 1977 to R. Gladstone. Further, the use of a device delaying the time of operation of the output device low level control is known from U.S. Pat. No. 3,366,095 issued Jan. 30, 1968 to M. De Leonardis. In this patent, the time delay function is performed by a bimetallic strip switch element which operates an output device in the form of alarm or input shutoff of some kind.
It is further well-known in the electrical arts that time delay may be accomplished by the use of resistive-capacitive (R-C) networks. Such delays have been incorporated into systems such as air conditioning to prevent too rapid cycling of the system following thermostatically controlled shutoff.